1. Field of Invention
This invention relates to packing materials formed as foamed pellets or peanuts for use as filler in shipping containers and other storage cartons. More particularly, the present invention pertains to such filler materials which are formed of starch composition, thereby providing biodegradability.
2. Prior Art
The increased interest in the environmental safety and biodegradability of packing materials has led to a variety of new products which dissolve harmlessly in water, rather than accumulate in landfills. For example, large volumes of packaging foam filler are produced and used to protect items in containers from damage during shipping. This high volume, foam filler has mainly been produced from polymers, such as polystyrene, which are not biodegradable. The accumulation of such polymers in landfills is of major concern because it occupies large volumes of space for the nominal weight of the product. Furthermore, these polymers do not readily degrade and therefore create long term difficulties for waste management. Attempts to burn these polymers generates noxious or toxic gases, further limiting disposal options. In addition to the adverse nature of the polystyrene polymers as a final product are the environmental hazards of their preparation. For example, chlorofluorocarbons (CFC's) used in the preparation of polystyrene foam, commonly called Styrofoam (registered trademark of Dow Chemical Co), are harmful to the earth's ozone layer.
Although these foamed polymers are useful in filling space as packing materials, their hydrophobic character tends to enhance electrostatic charge buildup. This is particularly true for the polystyrene materials which are often used as shipping material for electronic components. It is well known that such electrostatic accumulation poses a risk to much of the electronic equipment and software which may be affected by the presence of an electric field. It is not surprising, therefore, that substantial interest has developed in the use of starch composition as a substitute for polystyrene polymers, particularly in production of packing materials.
Starch offers several clear advantages over polymers previously used in this field. Starch is well known to be biodegradable and is a natural renewable resource that is produced in excess of the present market demand. Because starch is hydrophilic, it does not retain an electrostatic charge as occurs with hydrophobic polymers. Due to this hydrophilicity, packaging foam fillers prepared from starch can be readily dissolved in water as part of their natural decomposition. This obviously reduces their volume many times and allows them to be disposed in a normal waste water system.
Although starch has been used as protective packaging foam filler as disclosed in U.S. Pat. No. 4,863,655 and 4,900,361, general utility has not yet been commercially acceptable. Realization of acceptable resiliency, compressibility and low bulk density have required the use of starch which is derived from special plants that produce high amylose content, generally in excess of 45%, or which has been subjected to purification or modification procedures before being expanded by extrusion. The hydrophilic nature of starch materials creates some difficulties where moisture may degrade the packing materials, frustrating their function as a filler and causing unacceptable contamination of the products or equipment packed within the foamed material. Therefore, there remains a need for a foamed starch packing material which offers the desired resiliency, compressibility and low bulk density discovered in the polystyrene polymers, which retains these properties over extended time and which can be manufactured inexpensively with raw starch in a reproducible manner.